Methods of forming a semiconductor memory device

ABSTRACT

A method of metal doping a chalcogenide material includes forming a metal over a substrate. A chalcogenide material is formed on the metal. Irradiating is conducted through the chalcogenide material to the metal effective to break a chalcogenide bond of the chalcogenide material at an interface of the metal and chalcogenide material and diffuse at least some of the metal outwardly into the chalcogenide material. A method of metal doping a chalcogenide material includes surrounding exposed outer surfaces of a projecting metal mass with chalcogenide material. Irradiating is conducted through the chalcogenide material to the projecting metal mass effective to break a chalcogenide bond of the chalcogenide material at an interface of the projecting metal mass outer surfaces and diffuse at least some of the projecting metal mass outwardly into the chalcogenide material. In certain aspects, the above implementations are incorporated in methods of forming non-volatile resistance variable devices. In one implementation, a non-volatile resistance variable device in a highest resistance state for a given ambient temperature and pressure includes a resistance variable chalcogenide material having metal ions diffused therein. Opposing first and second electrodes are received operatively proximate the resistance variable chalcogenide material. At least one of the electrodes has a conductive projection extending into the resistance variable chalcogenide material.

This application is a continuation of application Ser. No. 09/797,635,filed on Mar. 1, 2001 now U.S. Pat. No. 6,727,192, which is incorporatedherein by reference.

TECHNICAL FIELD

This invention relates to non-volatile resistance variable devices andmethods of forming the same.

BACKGROUND OF THE INVENTION

Semiconductor fabrication continues to strive to make individualelectronic components smaller and smaller, resulting in ever denserintegrated circuitry. One type of integrated circuitry comprises memorycircuitry where information is stored in the form of binary data. Thecircuitry can be fabricated such that the data is volatile ornon-volatile. Volatile storing memory devices result in loss of datawhen power is interrupted. Non-volatile memory circuitry retains thestored data even when power is interrupted.

This invention was principally motivated in making improvements to thedesign and operation of memory circuitry disclosed in the Kozicki et al.U.S. Pat. Nos. 5,761,115; 5,896,312; 5,914,893; and 6,084,796, whichultimately resulted from U.S. patent application Ser. No. 08/652,706,filed on May 30, 1996, disclosing what is referred to as a programmablemetalization cell. Such a cell includes opposing electrodes having aninsulating dielectric material received therebetween. Received withinthe dielectric material is a fast ion conductor material. The resistanceof such material can be changed between highly insulative and highlyconductive states. In its normal high resistive state, to perform awrite operation, a voltage potential is applied to a certain one of theelectrodes, with the other of the electrode being held at zero voltageor ground. The electrode having the voltage applied thereto functions asan anode, while the electrode held at zero or ground functions as acathode. The nature of the fast ion conductor material is such that itundergoes a chemical and structural change at a certain applied voltage.Specifically, at some suitable threshold voltage, plating of metal frommetal ions within the material begins to occur on the cathode and growsor progresses through the fast ion conductor toward the other anodeelectrode. With such voltage continued to be applied, the processcontinues until a single conductive dendrite or filament extends betweenthe electrodes, effectively interconnecting the top and bottomelectrodes to electrically short them together.

Once this occurs, dendrite growth stops, and is retained when thevoltage potentials are removed. Such can effectively result in theresistance of the mass of fast ion conductor material between electrodesdropping by a factor of 1,000. Such material can be returned to itshighly resistive state by reversing the voltage potential between theanode and cathode, whereby the filament disappears. Again, the highlyresistive state is maintained once the reverse voltage potentials areremoved. Accordingly, such a device can, for example, function as aprogrammable memory cell of memory circuitry.

The preferred resistance variable material received between theelectrodes typically and preferably comprises a chalcogenide materialhaving metal ions diffused therein. A specific example is germaniumselenide with silver ions. The present method of providing the silverions within the germanium selenide material is to initially deposit thegermanium selenide glass without any silver being received therein. Athin layer of silver is thereafter deposited upon the glass, for exampleby physical vapor deposition or other technique. An exemplary thicknessis 200 Angstroms or less. The layer of silver is irradiated, preferablywith electromagnetic energy at a wavelength less than 500 nanometers.The thin nature of the deposited silver enables such energy to passthrough the silver to the silver/glass interface effective to break achalcogenide bond of the chalcogenide material, thereby effectingdissolution of silver into the germanium selenide glass. The appliedenergy and overlying silver result in the silver migrating into theglass layer such that a homogenous distribution of silver throughout thelayer is ultimately achieved.

It can be challenging to etch and to chemical-mechanical polish metal ision containing chalcogenide materials. Accordingly it would be desirableto develop memory cell fabrication methods which avoid one or both ofetching or polishing such materials. It would also be desirable todevelop alternate methods from that just described which incorporate themetal ions into chalcogenide materials. While the invention wasprincipally motivated in achieving objectives such as these, theinvention is in no way so limited. The artisan will appreciateapplicability of the invention in other aspects of processing involvingchalcogenide materials, with the invention only being limited by theaccompanying claims as literally worded and as appropriately interpretedin accordance with the doctrine of equivalents.

SUMMARY

The invention includes non-volatile resistance variable devices andmethods of forming the same. In one implementation, a method of metaldoping a chalcogenide material includes forming a metal over asubstrate. A chalcogenide material is formed on the metal. Irradiatingis conducted through the chalcogenide material to the metal effective tobreak a chalcogenide bond of the chalcogenide material at an interfaceof the metal and chalcogenide material and diffuse at least some of themetal outwardly into the chalcogenide material. In one implementation, amethod of metal doping a chalcogenide material includes surroundingexposed outer surfaces of a projecting metal mass with chalcogenidematerial. Irradiating is conducted through the chalcogenide material tothe projecting metal mass effective to break a chalcogenide bond of thechalcogenide material at an interface of the projecting metal mass outersurfaces and diffuse at least some of the projecting metal massoutwardly into the chalcogenide material. In certain aspects, the aboveimplementations are incorporated in methods of forming non-volatileresistance variable devices.

In one implementation, a non-volatile resistance variable device in ahighest resistance state for a given ambient temperature and pressureincludes a resistance variable chalcogenide material having metal ionsdiffused therein. Opposing first and second electrodes are receivedoperatively proximate the resistance variable chalcogenide material. Atleast one of the electrodes has a conductive projection extending intothe resistance variable chalcogenide material.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a semiconductor waferfragment in process in accordance with an aspect of the invention.

FIG. 2 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 2.

FIG. 4 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 3.

FIG. 5 is a view of the FIG. 1 wafer fragment at an alternate processingstep subsequent to that shown by FIG. 3.

FIG. 6 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 4.

FIG. 7 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 6.

FIG. 8 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Referring to FIG. 1, a semiconductor wafer fragment 10 is shown in butone preferred embodiment of a method of forming a non-volatileresistance variable device. By way of example only, example such devicesinclude programmable metalization cells and programmable opticalelements of the patents referred to above, further by way of exampleonly, including programmable capacitance elements, programmableresistance elements, programmable antifuses of integrated circuitry andprogrammable memory cells of memory circuitry. The above patents areherein incorporated by reference. The invention contemplates thefabrication techniques and structure of any existing non-volatileresistance variable device, as well as yet-to-be developed such devices.In the context of this document, the term “semiconductor substrate” or“semiconductive substrate” is defined to mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove. Also in the context of this document, the term “layer”encompasses both the singular and the plural unless otherwise indicated.Further, it will be appreciated by the artisan that “resistance setablesemiconductive material” and “resistance variable device” includesmaterials and devices wherein a property or properties in addition toresistance is/are also varied. For example, and by way of example only,the material's capacitance and/or inductance might also be changed inaddition to resistance.

Semiconductor wafer fragment 10 comprises a bulk monocrystallinesemiconductive material 12, for example silicon, having an insulativedielectric layer 14, for example silicon dioxide, formed thereover. Aconductive electrode material 16, also termed a first metal layer, isformed over and on dielectric layer 14. By way of example only,preferred materials include any of those described in the incorporatedKozicki et al. patents referred to above in conjunction with thepreferred type of device being fabricated. Layer 16 might constitute apatterned electrode for the preferred non-volatile resistance variabledevice being fabricated. Alternately by way of example only, layer 16might constitute a patterned line or extension of a field effecttransistor gate, with a subsequently deposited layer principally servingessentially as the electrode. An example preferred material for layer 16is elemental tungsten deposited to an exemplary thickness of from about100 Angstroms to about 1000 Angstroms. In the illustrated example, layer16 has been patterned, and another dielectric layer 17 has beendeposited and planarized as shown.

A second metal layer 18 is formed (preferably by a blanket deposition)on first metal layer 16. An exemplary preferred material in conjunctionwith the non-volatile resistance variable device being fabricated iselemental silver. A preferred thickness for layer 18 is from about 175Angstroms to about 300 Angstroms.

Referring to FIG. 2, second metal layer 18 is formed into a structure20, and first metal layer 16 is outwardly exposed. Such is preferablyconducted by subtractive patterning of metal layer 18, for example byphotolithographic patterning and etch. In one implementation, structure20 can be considered as comprising a metal mass projecting fromunderlying substrate material and having outer surfaces comprised of atop surface 22 and opposing side surfaces 24 which join with top surface22 at respective angles. The preferred angles are preferably withinabout 15° of normal, with normal angles being shown in the figures.

Referring to FIG. 3, a chalcogenide material 26 is formed over thesubstrate on second metal structure 20 outer surfaces 22 and 24, and onexposed first metal layer 16. Such is preferably formed by blanketphysical vapor deposition. A preferred deposition thickness for layer 26is preferably less than three times the thickness of deposited layer 18,with an example being from about 525 Angstroms to about 900 Angstroms.More preferred is a thickness to provide layer 18 at 20% to 50% of layer26 thickness. Exemplary preferred chalcogenide materials include thosedisclosed in the Kozicki et al. patents referred to above. Specificpreferred examples include a chalcogenide material having metal ionsdiffused therein represented by the formula Ge_(x)A_(y), where “A” isselected from the group consisting of Se, Te and S and mixtures thereof.The illustrated example provides but one possible example of surroundingthe exposed outer surfaces of a projecting metal mass with chalcogenidematerial in accordance with but one aspect of the invention.

Referring to FIG. 4, irradiating is conducted through chalcogenidematerial 26 to patterned second metal 18 effective to break achalcogenide bond of the chalcogenide material at an interface with thepatterned second metal outer surfaces and the chalcogenide material, andto diffuse at least some of second metal 18 outwardly into thechalcogenide material. Metal doped material 27 is formed thereby.Therefore as shown in the preferred embodiment, only a portion ofblanket deposited chalcogenide material layer 26 is doped with secondmetal 18. A preferred irradiating includes exposure to actinic radiationhaving a wavelength below 500 nanometers, with radiation exposure atbetween 404-408 nanometers being a more specific example. A specificexample: in a suitable UV radiation flood exposure tool is 4.5 mW/cm²,15 minutes, 405 nm wavelength, at room ambient temperature and pressure.

In the depicted and preferred embodiment, the irradiating diffuses onlysome of the metal from layer 18 outwardly into chalcogenide material,leaving a remnant structure 20 a. Accordingly, the projecting metal mass20 a has a shape after the irradiating which is maintained in comparisonto original shape 20, but at a reduced size. FIG. 5 illustrates a lesserpreferred alternate embodiment 10 a whereby the irradiating and/or layerdimensions might be modified such that the irradiating diffuses all ofprojecting metal mass 20 outwardly into the chalcogenide material.

The preferred exemplary tungsten material of layer 16 does notappreciably diffuse into layer 26. Referring to FIG. 6 and regardless,chalcogenide material 26 not doped with metal 18 is substantiallyselectively etched from metal doped portion 27 of the chalcogenidematerial. In the context of this document, “substantially selective”means a relative etch ratio of layer 26 relative to layer 27 or at least3:1. In the illustrated and preferred embodiment, such etching ispreferably conducted to remove all of chalcogenide material 26 which hasnot been doped with metal 18. The preferred etching comprises dryanisotropic etching, preferably dry plasma anisotropic etching. Aprinciple preferred component of such etching gas comprises CF₄.Additional preferred gases in the chemistry include C₂F₆ and C₄F₈. Toppower is preferably maintained at 500 watts, with the lower wafersusceptor being allowed to float. Susceptor temperature is preferablymaintained at about 25° C., and an exemplary reactor pressure is 50mTorr. By way of example only, a specific example in a reactive ionetcher is CF₄ at 50 sccm, Ar at 25 sccm, susceptor temperature at 25°C., pressure of 50 mTorr and top power at 500 Watts.

Referring to FIG. 7, an insulating layer 30 has been deposited and metaldoped chalcogenide material 27 has been exposed. An example andpreferred material for layer 30 is silicon nitride.

Referring to FIG. 8, an outer conductive electrode layer 32 has beendeposited and patterned to form the outer electrode of the preferrednon-volatile resistance variable device. Example materials include thosedisclosed in the above Kozicki et al. patents. In the illustrated anddescribed preferred example, silver structure 20 a might be designed andfabricated to constitute the effective quantity of silver forprogramming the device with no silver being provided in electrode 32.Alternately by way of example only, layer 16 might also constituteelemental silver with no silver being provided in electrode 32. Further,by way of example only, electrode 32 might principally compriseelemental silver, or at least a lower silver portion in contact with thechalcogenide material 27.

The above-described preferred embodiment example was in conjunction withfabrication of a non-volatile resistance variable device. However, theinvention also contemplates metal doping a chalcogenide materialindependent of the device being fabricated, and in the context of theaccompanying claims as literally worded regarding methods of metaldoping a chalcogenide material. Further, the preferred example is withrespect to formation of a projecting metal from an underlying substratehaving chalcogenide material received thereover. However, the inventionis in no way so limited and also contemplates, by way of example only,diffusing metal from an entirely flat, or other, underlying surface intooverlying chalcogenide material.

The invention also contemplates non-volatile resistance variable devicesindependent of the method of manufacture. In one implementation, such adevice includes a projecting metal mass (for example mass 20 a)extending outwardly from a first metal layer laterally central intoresistance variable chalcogenide material. In one aspect, the inventioncontemplates the device being in a highest resistance state for a givenambient temperature and pressure. For example, the FIG. 8 device asdepicted is in such a highest state of resistance. Progressively lowerstates of resistance for a given ambient temperature and pressure willexist as a silver dendrite, in the preferred embodiment, progressivelygrows from an electrode to the point of contacting the opposingelectrode. FIG. 8 depicts but one exemplary embodiment of such anon-volatile resistance variable device having such a laterally centrallocated projecting mass relative to material 27.

The invention also contemplates a non-volatile resistance variabledevice in a highest resistance state for a given ambient temperature andpressure independent of a conductive projection which is so centrallylocated. Such comprises a resistance variable chalcogenide materialhaving metal ions diffused therein. Opposing first and second electrodesare received operatively proximate the resistance variable chalcogenidematerial, with at least one of the electrodes comprising a conductiveprojection extending into the resistance variable chalcogenide material.Provision of such a structure is in no way shown or suggested in ahighest resistance state for a given ambient temperature and pressure inany of the teachings and drawings of the above-described Kozicki et al.patents.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of forming a semiconductor memory device comprising: forminga metal over a substrate; patterning said metal into a structure havingan outer surface; blanket depositing a chalcogenide material over saidsubstrate and on said metal structure outer surface; diffusing a portionof said patterned metal outwardly into a portion of said chalcogenidematerial; and etching a portion of said chalcogenide material into whichsaid patterned metal has not been diffused.
 2. The method of claim 1wherein said blanket depositing said chalcogenide material compriseschemical vapor deposition.
 3. The method of claim 1 wherein said formingsaid metal comprises blanket deposition.
 4. The method of claim 1wherein said portion of said patterned metal diffused outwardly intosaid chalcogenide material comprises less than all of said patternedmetal.
 5. The method of claim 4 wherein the portion of said patternedmetal not diffused outwardly into said chalcogenide material is smallerbut substantially the same shape as said patterned metal before saidportion of said patterned metal is diffused outwardly into saidchalcogenide material.
 6. The method of claim 1 wherein said portion ofsaid patterned metal diffused outwardly into said chalcogenide materialcomprises all of said patterned metal.
 7. The method of claim 1 whereinthe step of diffusing a portion of said patterned metal outwardly intosaid chalcogenide material comprises irradiating through saidchalcogenide material to said patterned metal.
 8. The method of claim 7wherein said irradiating comprises irradiating through said chalcogenidematerial to said patterned metal with electromagnetic radiation having awavelength less than 500 nanometers.
 9. The method of claim 8 whereinsaid electromagnetic radiation has a wavelength of about 404 nanometersto about 408 nanometers.
 10. The method of claim 8 wherein saidelectromagnetic radiation has a wavelength of about 405 nanometers. 11.The method of claim 1 wherein said etching comprises dry anisotropicetching.
 12. The method of claim 1 wherein said etching comprises dryanisotropic etching using a gas chemistry comprising CF₄.
 13. A methodof forming a semiconductor memory device comprising: forming a patternedmetal structure having an outer surface over a substrate; blanketdepositing a chalcogenide material on said patterned metal structureouter surface; diffusing a portion of said patterned metal outwardlyinto a portion of said chalcogenide material; and etching a portion ofsaid chalcogenide material into which said patterned metal has not beendiffused.
 14. The method of claim 13 wherein the step of forming apatterned metal structure having an outer surface comprises the stepsof: forming a metal over a substrate; and patterning said metal into astructure having an outer surface.
 15. The method of claim 13 whereinthe step of diffusing a portion of said patterned metal outwardly intosaid chalcogenide material comprises irradiating through saidchalcogenide material to said patterned metal.
 16. The method of claim15 wherein said irradiating comprises irradiating through saidchalcogenide material to said patterned metal with electromagneticradiation having a wavelength less than 500 nanometers.
 17. The methodof claim 16 wherein said electromagnetic radiation has a wavelength ofabout 404 nanometers to about 408 nanometers.
 18. The method of claim 16wherein said electromagnetic radiation has a wavelength of about 405nanometers.
 19. A method of forming a semiconductor memory device, saidmethod comprising: forming a first electrode over a semiconductorsubstrate; forming a metal layer over said first electrode; forming alayer comprising a chalcogenide material over said first electrode andsaid metal layer; irradiating said metal layer to diffuse at least aportion of metal ions from said metal layer into portions of saidchalcogenide layer, wherein said chalcogenide layer comprises a firstregion with metal ions diffused therein and a second region without asubstantial amount of metal ions diffused therein; removing said secondregion of said chalcogenide layer, wherein said first region of saidchalcogenide layer remains; and forming a second electrode over at leasta portion of said remaining first region of said chalcogenide layer. 20.A method of forming a semiconductor memory device comprising: forming afirst metal layer over a semiconductor substrate; forming a second metallayer over said first metal layer; forming a chalcogenide layer oversaid first and second metal layers; diffusing a portion of said secondmetal layer into a portion of said chalcogenide material to form a firstand second region, wherein said first region comprises metal ions fromsaid second metal layer; and removing said second region from saidchalcogenide material.